1. Field of the Invention
The invention relates to reliable solid-state pulse generators for generating repetitively short, high power pulses with relatively fast rise times.
2. Description of the Related Art
High voltage pulse generators, with relatively fast rise-times, are typically used to drive gas discharge loads such as lasers and discharge devices for pollution control applications. In the past, such pulse generators used thyratrons to generate the desired pulses. However, thyratrons are relatively unreliable, relatively heavy, and require complex electrical control systems. Solid state devices, although lighter and potentially more reliable than thyratrons, can switch less power on a per-device basis, Thus, a number of solid state devices are needed to replace a single thyratron. In some configurations where many solid-state devices are connected together, failure of one solid-state device can trigger the failure of many devices in the circuit. Moreover, solid state devices, although potentially more reliable than thyratrons, are relatively less tolerant of over-voltage and/or over-current transients. Solid state devices can be permanently damaged by a single over-voltage transient lasting only a few nanoseconds. In many pulse generators, the solid-state devices are used to drive an inductive load such as a transformer. Inductive loads are prone to generate voltage spikes when the current through the inductor is suddenly switched off (as typically occurs at the end of a pulse). These voltage spikes can destroy solid-state devices and render the pulse generator inoperable.
The present invention solves these and other problems by providing a solid-state drive circuit to drive a split magnetic core transformer. In one embodiment, the solid-state drive circuit uses MOSFETs to achieve desirable pulse characteristics. In one embodiment, the solid-state drive circuit uses a blumlein to produce a desired input pulses in a primary winding of the split magnetic core. In one embodiment, ferrite beads are used to further shape the pulse produced by the blumlein.
In one embodiment, the pulse length is determined not by the xe2x80x9conxe2x80x9d time of a solid state device, but, rather, by the characteristics of the blumlein and the split core transformer. Since the solid-state devices do not determine the pulse length, the xe2x80x9conxe2x80x9d time of the solid-state devices can exceed the pulse length. When the solid-state devices are finally turned off, no damaging voltage spike is generated because the current through the inductors (e.g., the current through the transformer) is negligible. This protects the solid-state devices from harmful voltage spikes and simplifies the drive circuits for the solid-state devices (since the solid-state device can be driven by a relatively long pulse).
The use of a split magnetic core allows several solid-state drive circuits to be used in parallel to produce a single output pulse. In one embodiment, the split magnetic core is configured as an inductive adder. The split magnetic core combines the output from several solid-state drive circuits in a manner that leaves the drive circuits relatively isolated from one another. This relative isolation reduces the chance that a failure in one solid-state drive circuit will cause failures in other solid state drive circuits.
In one embodiment, each solid-state drive circuit drives a separate primary winding of a split magnetic core transformer. In one embodiment, the primary windings are low-impedance single-turn windings. In one embodiment, each core of the split core transformer has one primary winding. In one embodiment, the separate cores of the split core transformer are provided with a single secondary winding that couples all of the cores. In one embodiment, the secondary winding is a multi-turn winding. In one embodiment, the number of turns in the secondary winding is selected to match the output impedance of the transformer to the impedance of the load, thereby providing increased power to the load.
In one embodiment, the solid-state drive circuits and the split magnetic core are constructed on a modular basis such that any one (or any pair) of the solid-state drive circuits can be easily replaced without disassembling the split magnetic core.
As compared to a thyratron, the solid-state pulsed power generator provides a relatively higher repetition rate, improved lifetime, reduced weight, simplified electrical control system, and reduced electrical power requirements.
In one embodiment, the pulse power generator is used to produce pulsed electrical fields for medical and biomedical applications. In one embodiment, the pulse power generator is used to produce pulsed electrical fields for plasma exhaust treatment systems for automobiles and other vehicles.